Salt solution mining and geothermal heat utilization system

ABSTRACT

A METHOD OF SOLUTION MINING AND RECRYSTALLIZATION RECOVERY OF SOLID SODIUM CHLORIDE SALT FORM UNDERGROUND OCCURRENCES THEREOF, WHICH UTILIZES THE LHEAT CONDUCTIVITY CHARACTERISTICS OF AN UNDERGROUND SALT SPINE, SPIRE, DOME, OR THE LIKE; WHEREBY THE LATEN HEAT OF THE EARTH&#39;&#39;S CORE MAY BE EFFICIENTLY EMPLOYED IN THE RECRYSTALLIZATION PROCESS. THE HIGHLY (HEAT) CONDUCTIVE CHARACTERISTIC OF A SALT SPIRE OR THE LIKE SUCH AS HAS BEEN FORMED BY GEOLOGIC PLASTIC FLOW AND VERTICAL INTRUSION OF A PORTION OF A DEEPSEATED &#34;MOTHER&#34; BED OF SALT THROUGH THE RELAVIVELY HEATINSULATIVE OVERLYING ROCK STRATA, IS EMPLOYED TO DRAW HEAT FROM A HIGH TEMPERATURE GEOLOGIC STRUCTURE WHICH IS SO DEEP-SEATED AS TO BE ECONOMICALLY INACESSIBLE TO MODERN DRILLING EQUIPMENT. THIS HEAT ENERGY IS DRAWN INTO A &#34;HEAT WELL&#34; WHICH DEVELOPED AT AN UNDERGROUND LEVEL WHICH IS READILY WITHIN REACH OF MODERN EARTH BORE DRILLING TECHNIQUES; THE HEAT ENERGY FLOWING INTO THE &#34;HEAT WELL&#34; BEING THEREUPON TRANSMITTED AND UTILIZED INTHE SALT RECRYSTALLIZATION PROCESS FACILITY AT OR NEAR THE EARTH&#39;&#39;S SURFACE.

July 11, 1972 c. H. JACOBY 3,676,078

SALT SOLUTION MINING AND GEOTHERMAL HEAT UTILIZATION SYSTEM Filed March 1.9, 1970 3 Sheets-Sheet l MOTHER BED OF sA LT' I .\'\E.\'TOR.

CHARLES H JACOBY A TTORNE Y5 y 11, 1972 c. H. JACOBY 3,676,078

SALT SOLUTION MINING AND GEO'IHERMAL HEAT UTILIZATION SYSTEM Filed March L9, 1970 3 Sheets-Sheet 2 Z OVERBURDEN g a VI CAP ROCK INVENTOR.

CHARLES H. JACOBY BY A T TORNE Y5 11, 1972 c. H.JACOBY 3,676,078

SALT SOLUTION MINING AND GEOTHERMAL HEAT UTILIZATION SYSTEM Filed March 19, 1970 3 Sheets-Sheet 5 INVENTOR.

CHARLES H. JACOBY @am 9 @"Am ATTORNE f5 United States Patent 3,676,078 SALT SOLUTION MINING AND GEOTHERMAL HEAT UTILIZATION SYSTEM Charles H. Jacoby, Dalton, Pa., assignor to International Salt Company, Clarks Summit, Pa. Filed Mar. 19, 1970, Ser. No. 21,051 Int. Cl. B01d 1/00, 11/02; C01d 3/08 US. Cl. 23-299 4 Claims ABSTRACT OF THE DISCLOSURE A method of solution mining and recrystallization recovery of solid sodium chloride salt from underground occurrences thereof, which utilizes the heat conductivity characteristics of an underground salt spine, spire, dome, or the like; whereby the latent heat of the earths core may be efficiently employed in the recrystallization process. The highly (heat) conductive characteristic of a salt spire or the like such as has been formed by geologic plastic flow and vertical intrusion of a portion of a deepseated mother bed of salt through the relatively heatinsulative overlying rock strata, is employed to draw heat from a high temperature geologic structure which is so deep-seated as to be economically inaccessible to modern drilling equipment. This heat energy is drawn into a heat well which is developed at an underground level which is readily within reach of modern earth bore drilling techniques; the heat energy flowing into the heat well being thereupon transmitted and utilized in the salt recrystallization process facility at or near the earths surface.

BACKGROUND AND GENERAL DESCRIPTION OF THE PRESENT INVENTION Whereas numerous proposals have been previously made whereby to employ so-called underground heat to useful purposes, certain practical limitations have invariably minimized the economic importance and/ or commercial success of such efforts. This has been due to such factors as the relatively low and fluctuating temperatures available from so-called hot underground water or steam well sources such as have been suggested for such purposes, as well as their unreliability and depletion-prone characteristics. Also, the expense and difficulties attending attempted bore hole operations through ordinarily encountered geologic structures with a view to reaching such depths as would tap rock formations competent to support a constant and sufliciently high temperature heat abstracting operation have proved prohibitive. For examples of such prior proposals see Pats. 2,461,449; 3,140,986; 3,274,- 769; and 3,363,664.

The present invention derives from the discovery that certain geological spines or spires or domes comprising solid masses of crystalline rock salt which rarely, but in some places within the earths crust structure, intrude upwardly from deep-seated mother beds towards the earths surface to within reach of modern drilling equipment and are highly heat conductive compared to the surrounding and/or more ordinarily encountered underground strata. These geologic phenomena are sometimes integrally connected in thermal continuity with intensely hot mother beds of salt or other rock masses which are located at such great distances underground as to be far beyond reach of modern drilling techniques. Thus, in such cases these salt domes or spires are uniquely adapted to function as conduits for transmission of practically unlimited quantities of heat from the earths core and into and through the earths crust structure to the extent they penetrate the latter.

By virtue of the present invention a bore hole driven into a salt dome only to a depth of the order of 10,000 or 3,676,078 Patented July 11, 1972 15,000 feet may tap a constant high temperature heat energy supply drawing from sources as deep as 50,000 or feet or more. Such results are attainable because of the fact that rock salt structures have heat conductivity coefficients many times higher than the coefiicients of other geologic structures such as are usually encountered by underground drilling. See Handbook of Physical Constants, revised edition, published by the Geological Society of America, Inc., pp. 461-466. Test data has established, for example, that a bore hole drilled into a Louisiana Gulf Coast salt dome to a depth of 12,000 feet will tap a practically unlimited source of heat at 270 to 310 F., depending upon the proximity of the bore hole to the edge of the dome. Such sources of heat are not obtainable at the same depth by drilling into the usually encountered underground geology.

This invention utilizes the existence of this rare heat supply and conduction facility in combination with the fact that a salt spire of the character described may be easily reached and penetrated to suitable depths by modern bore hole drilling equipment. A heat cavity may be thereby economically constituted to provide a suitable heat supply reservoir; such as for example by solution mining a desirably sized and shaped cavity in the rock salt mass. The subsequently emptied cavity or heat Well may then be flushed for heat abstraction purposes by circulating a heat exchange fluid therethrough, such as any inert (to salt) gas or liquid. It is of particular importance that when the system contemplated by the present invention is properly managed, the heat well may be maintained to be leakproof and constant as to size and shape. Hence, a uniform and regulatable rate of heat extraction and delivery to the surface facility should be maintained.

DETAILED DESCRIPTION In accordance with one example of the present invention a heat spire as above described and occurring within reach of modern drilling equipment is first located by test drilling or other means; and a heat reservoir is then established in a hot portion thereof by drilling one or more bore holes into the spire to such depth as to reach a constant source of heat at the desired temperature. A heat exchange cavity is then formed in the spire, and is established in fluid circulation communication (at monitored rates) with conduit means extending from above ground. Thus, a regulated supply of relatively cool fluid may be circulated through the cavity as to become suitably heated therein, and is then conducted back up to an aboveground (or perhaps underground) facility, for utilization of the heat energy abstracted by the fluid from the salt mass. The fluid may be in the form of any chemically neutral and non-dissolving (to the salt) heat exchange medium.

Inasmuch as competent (permanently sized and shaped and leakproof) cavities may be economically formed in such salt domes or spires by currently available solution mining techniques, and advantageously in close association with a field of solution mining salt Wells, the heat abstracted by a heat cavity of the present invention may be most beneficially utilized in the process of evaporating or recrystallizing or otherwise processing the brines produced by the associated brine field. The invention furthermore contemplates improved techniques for transmission of a heat-exchange fluid through the heat cavity of the system.

Specifically, the invention contemplates automatically controlled circulation of the heat exchange fluid through the conduit and heat exchange cavity system at such rate as to cause delivery of the heat exchange fluid uniformly at the desired temperature to the heat utilization facility. In this respect the system will be automatically monitored by temperature sensors at the output end of the conduit system, controlling velocity of fluid flow through the heat exchange cavity. Note that the conduit system may be self-moving; the relatively cooler fluid in the down-hole outweighing the relatively hotter fluid in the up-hole. However, in order to positively establish and maintain circulation, a priming pump may be employed and kept on a standby basis and brought automatically into play whenever needed by means of a motor control actuated in response to signals from a rate-of-flow meter in the conduit line. It is also contemplated that if the heat utilizing facility is located near a source of brackish water such as sea water or the like, this may be used as the solvent for the solution mining operation; the evaporation vapor effluent thereupon providing good potable water.

Whereas the invention may be applicable to a variety of solution mining systems, it is illustrated and described in detail hereinafter by way of example in conjunction with a sodium chloride rock salt solution mining operation; as will be more fully explained and as is illustrated by the accompanying drawing wherein:

THE DRAWING FIG. 1 is a vertical geologic sectional view, illustrating a typical system installation in accordance With the present invention;

FIG. 2 is a fragmentary enlarged scale view of an upper portion of FIG. 1; and

FIG. 3 is a flow diagram of the system illustrated by FIGS. 1-2.

As shown in FIG. 1, in accordance with the present invention, a relatively rarely occurring geological phenomenon known as a salt spire or dome as indicated at occurring in thermal continuity with a deep-seated mother bed" is first located and then penetrated from an appropriate location at the earths surface by means of a bore hole system which is designated generally at 12. The penetration is conducted to a relatively great depth; say, of the order of 10,000 to 20,000 feet below the earths surface, such as may be required to acquire a heat reservoir cavity as indicated at 14 at a level wherein temperatures approximating 300 F. or higher are encountered within a substantial body of solid rock salt. It is essential that the reservoir be located in an integral structure having thermal continuity with the heat source mother bed; all components of the system having such thermal continuity and conductivity characteristics as will insure continuous replacement of the anticipated heat energy abstraction from the reservoir.

'Because of the solubility characteristics of rock salt, the heat reservoir 14 may be conveniently and economically formed at the desired level in the spire 10 by flowing a stream of water from the surface to the bottom of the bore hole system, and then counterflowing the resultant brine solution upwardly to the earths surface for disposal. A circulation system for this purpose may be established either within a single bore hole as illustrated at 12 (FIG. 1) by use of concentric casings; or, alternatively it may be arranged as shown in FIG. 2 by use of a pair of parallel bore holes 16, 17, as explained for example in my earlier Pats. Nos. 3,42l,794; 3,348,883; 3,386,768; and Re. 25,682.

As previously stated, the invention contemplates particular advantages when employed in conjunction with a salt mining operation such as may comprise one or more solution mining cavities as are illustrated in FIG. 1 at 18, 19. As shown therein the mining cavities may be serviced as indicated generally at 20-21 either by multiple cased single bore holes, or by dual bore holes, as indicated at 22, 24 (FIG. 2). The heat cavity bore hole system 12 is illustrated as being coupled to a surface facility which is indicated generally at 25, while the salt brine production cavities are illustrated by way of example as being arranged to be serviced by earth surface facilities as are indicated generally at 26, 28, respectively.

It is a particular feature of the present invention that the heat cavity 14 is located within a structurally solid portion of the salt spire 10, and at such a depth therein as to operate as a heat well for reception and transmission of the heat energy which is constantly available for conduction from the earths core for example by way of the mother bed of salt forming the foundation for the spire 10. Thus, the cavity 14, after being suitably formed by a solution mining process and then emptied, provides a heat exchange chamber through which a heat exchange fluid such as a suitable gas or liquid may be transported by pumping it downwardly through the casing 16 (FIG. 2) and permitting it to rise through the casing 17 after it flows in heat exchange relation around and against the walls of the heat cavity.

As illustrated diagrammatically at FIG. 3, a typical rock salt solution mining and recrystallization recovery system as contemplated in conjunction with the present invention will comprise a solution mining cavity 19 into which a solvent liquid such as water or dilute brine may be introduced by means of a pump, whereby a concentrated brine from the cavity 19 will be forced to flow upwardly through the well bore conduit 24 (FIG. 2) to the surface plant. Here it is delivered into the evaporator apparatus for recovery of the salt product therefrom in accordance with any preferred form of a variety of technologies, such as are discussed for example in my earlier Pats. 3,348,883; 3,386,786; and 3,421,794. Still further by way of example the vapor eflluent from the salt recovery apparatus may then be passed through a condenser for recovery of a fraction of the pure water therefrom; the residual efiiuent being returned to the conduit supplying the pump servicing the injection well bore 22. Dilute brine eflluent from the recovery system and/or make up fresh water may be added to the pump supply conduit, as needed. Furthermore, as stated hereinabove, if the solution mining and salt recovery facility is located in the region of a supply of nonpotable water such as sea water or other brackish water or the like, and if the impurities therein would not add prohibited contaminants to the salt product of the system such nonpotable water may be utilized as Whole or part of the solvent in the solution mining operation. In such case the condenser unit will then deliver a potable water supply such as may be of economic importance.

In any case, in accordance with the present invention the heated fluid ascending the output well bore conduit 17 from the heat exchange cavity 14 will be utilized to heat power the evaporator apparatus referred to hereinabove; thereby eliminating need for any fuel burning heat generating facility. As illustrated in FIG. 3, the spent heat exchange fluid exiting from the evaporator apparatus is recirculated through the heat recovery well 14 by means of a pump delivering fluid to the well bore conduit 16.

It is a particular feature of the present invention that the heat exchange fluid to be used is of such nature as to be non-dissolving and chemically inert as to the rock salt wall structure of the heat cavity 14, and that the fluid is circulated through the cavity at such rate as to abstract heat from the walls thereof at such rate that when the fluid passes through the evaporator apparatus it delivers heat energy thereto uniformly at the desired rate and temperature. Accordingly, in order to suitably regulate the rate of heat exchange fluid flow a meter system is arranged in conjunction with the heated fluid delivery conduit. Rate of fluid flow and temperature sensors deliver signals to a monitoring mechanism, the output from which is arranged to regulate the performance of the pump. It will be appreciated that the overriding parameter controlling the monitoring operation for most effective operation of the evaporator apparatus will be the permissive input temperature fluctuation range of the fluid as it enters the evaporator apparatus.

As stated hereinabove, the heat exchange fluid may comprise any medium of high heat transfer characteristics. Accordingly, some of the relatively expensive organic chemical compositions may be preferred for this use, and in such case the fluid circulating conduit system will of necessity be maintained in leak-proof condition. The rock salt wall structure of the heat cavity 14 being outstandingly competent in regard to its fracture-free and leak-proof characteristics, renders such a closed circuit system fully feasible and practical. Examples of liquids contemplated as being suitable for this purpose are: ethylene glycol, carbon tetrachloride, propylene glycol, hexane, diphenyl, diphenyl ether, polyoxyethylene glycols, mineral oils, kerosenes, block copolymers of ethylene glycols and propylene glycols, glycerol, polypropylene diols, and suitable higher fatty acids, alcohols, esters and ethers. Also, condensible gases may be employed, such as dichlorodi- :Eluoromethane and other Freons, propane, carbon dioxide and chlorine. These may be employed alone or in mixture with other such fluids to produce the desired operative heat transfer means.

I claim:

1. The method of solution mining and recovering solid sodium chloride from an underground occurrence thereof, which method comprises the steps of:

(a) determining the location of a rock salt formation which extends to a depth inaccessible by bore drilling techniques and into thermal continuity with a bed of elevated temperature material;

.(b) driving a bore hole into said rock salt formation to a selected accessible depth of at least 10,000 feet at which the temperature of the rock salt and the rate of heat transfer thereto available from said bed of elevated temperature material are of selected values;

(c) dissolving said rock salt through said bore hole for a time sufficient to produce, at said selected accessible depth, a cavity of selected size having a heat transfer area which will provide a selected rate of heat energy due to said selected values of temperature and heat transfer rate specified in (b);

(d) flushing said cavity through said bore hole with a fluid which is non-soluble and inert chemically with respect to said rock salt formation to terminate the dissolution and retain said selected size of the cavity;

(g) circulating heat transfer fluid which is non-soluble and inert with respect to said rock salt formation through the bore hole of step (b) at a rate suflicient to evaporate the brine of step (f);

(h) thermally contacting the heat transfer fluid of step (g) with the brine of step (f) to evaporate the latter; and

,(i) recovering solid sodium chloride from the evaporation of step (h).

2. The method according to claim 1 including the step of condensing vapor obtained from step (h) and recycling same as solvent for step (f).

3. The method according to claim 1 wherein the heat transfer fluid of step (g) is circulated in a closed path and including the step of controlling the return flow of said heat transfer fluid in accord with its emergent temperature.

4. The method according to claim 3 including the step of condensing vapor obtained from step (h) and recycling same as solvent for step (f).

References Cited UNITED STATES PATENTS 1,917,154 7/1933 Porter 1591 G 2,461,449 2/1949 Smith 159- 1 G 3,140,986 7/1964 Hubbard -26 3,274,769 9/1966 Reynolds 1591 G 3,278,234 10/1966 Helvenston 299-5 3,348,883 10/ 1967 Jacoby 299--4 3,386,768 6/1968 Jacoby 2995 3,421,794 1/ 1969 Jacoby 2995 3,432,205 3/ 1969 Hottman 2994 3,433,530 3/1969 Dahms 2994 3,470,943 10/ 1969 Van Huisen 159-1 G FOREIGN PATENTS 313,257 6/1919 Germany 159-1 G 498,700 5/1930 Germany 159--1 G OTHER REFERENCES Scientific American, Oct. 27, 1917, vol. 117, No. 17, 2 pages.

Science and Mechanics, October 1951, pp. -97.

NORMAN YUDKOFF, Primary Examiner S. I. EMERY, Assistant Examiner US. Cl. X.R.

23403, 306,312 AH; 159 1 G; 299- s; 60-26; 45; e1- .s; 62-260 

